The present invention relates to an external screening device for a pivotable skylight window with a horizontal axis of rotation of a sash in a centre area of the main frame of the window, comprising a continuous flexible screen which is wound on a roller situated at an upper horizontal frame portion of the window and is connected at its free end with a bottom bar guided in side guide rails, said bottom bar being connected for unrolling the screen over a cord drive with a drive unit which is also positioned in connection with the upper horizontal frame portion, said side guide rails for the bottom bar extending along the parts of the frame side portions placed above the axis of rotation and the parts of the sash side portions placed below the axis of rotation.
The two-part design of the side guide rails with upper sections running along the top part of the frame side portions and lower sections running along lower parts of the sash side portions is known per se from U.S. Pat. No. 4,691,753 for a screening device in the form of a roller shutter with relatively rigid slats guided in the side guide rails. The document as such deals with a design of the control cables which prevent jamming of the rigid slats in the guide rails.
From U.S. Pat. No. 1,583,133 there is known a screening device with a flexible material which is guided in hinged side rails and has rigid supporting rods for preventing sagging of the screening material. This screening device is not intended for a pivotable window, and the hinged guiding rails are, when in use, mounted on a window frame or equivalent in an aligned manner. The hinge itself is only used for folding the guide rails during shipment so as to save space. During shipment the flexible material is not present in the guide rails but wound on a roller.
If an external screening made of a flexible web is used in connection with a pivotable skylight window, eg. as shown in FIG., 1, where the lower portion of the window sash below the axis of rotation is turned outwards under an angle with the frame of typically between 10.degree. and 60.degree., it is a problem that the screening web which extends between the upper horizontal frame portion and the lower horizontal sash portion shows a pronounced tendency to flutter or flap even by minor wind loads which partly involves the risk of wear and tear of the web, partly makes an annoying noise, while at the same time the esthetic appearance is deteriorated and light may penetrate through the uncovered opening between the web and the frame/sash construction.
Furthermore, when the window is closed, such screening devices have a tendency in a drawn-out condition and with a wet web to make the web stick to the pane which again, especially when seen from the inside, provides a severely deteriorated esthetic appearance and in addition can entail problems with rewinding the web on the roller.